This application claims the benefit of a Japanese Patent Application No. 11-351986 filed Dec. 10, 1999, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to magnetic recording media and magnetic storage apparatuses, and more particularly to a magnetic recording medium and a magnetic storage apparatus for carrying out a high-density longitudinal magnetic recording.
2. Description of the Related Art
The storage capacity of longitudinal magnetic recording media has been rising rapidly due to reduction of media noise and the development of magneto-resistive and high-sensitivity spin-valve heads.
A typical magnetic recording medium includes a substrate, a seed layer, a Cr or Cr-based underlayer, a Co-based magnetic layer where the information is written, a C or Diamond-Like C (DLC) overlayer, and an organic lubricant layer which are successively stacked in this order.
Lowering the media noise involves decreasing the grain size and size distribution of the magnetic layer, by reducing the magnetic layer thickness. It is possible to reduce the magnetic layer thickness by the proper use of an underlayer made of CrMo or NiAl, for example, and by the use of an intermediate layer which is disposed between the underlayer and the magnetic layer and is made of CrTiB, for example. By lowering the media noise, it becomes possible to improve the signal-to-noise ratio (SNR) and to achieve high-density recording.
The underlayer also promotes crystallographic c-axis orientation of the magnetic layer in a plane which increases the remanent magnetization and the thermal stability of bits. In order to obtain a satisfactory crystallographic c-axis orientation of the magnetic layer, the underlayer thickness must be set relatively large, since a thin underlayer deteriorates the crystallographic c-axis orientation of the magnetic layer. However, the grain size distribution of the magnetic layer usually follows the grain size distribution of the underlayer, and the underlayer grain size has a dependence on the underlayer thickness such that the underlayer grain size increases as the underlayer thickness increases. In other words, in order to decrease the grain size and size distribution of the magnetic layer, it is necessary to reduce the underlayer thickness.
Therefore, the conventional magnetic recording medium had a problem in that the control of the underlayer thickness leads to a tradeoff between the crystallographic c-axis orientation of the magnetic layer and the grain size and size distribution of the magnetic layer. That is, the crystallographic c-axis orientation of the magnetic layer can be improved by increasing the underlayer thickness, but this results in increased grain size and size distribution of the magnetic layer. On the other hand, the grain size and size distribution of the magnetic layer can be improved by reducing the underlayer thickness, but this results in deteriorated crystallographic c-axis orientation of the magnetic layer.
Accordingly, it is a general object of the present invention to provide a novel and useful magnetic recording medium and magnetic storage apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention to provide a magnetic recording medium and a magnetic storage apparatus which can satisfactorily control both the crystallographic c-axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.
Still another object of the present invention is to provide a magnetic recording medium comprising a substrate, and a magnetic layer disposed above the substrate, wherein the magnetic layer has an initial layer on a side closer to the substrate, and a final layer on a side opposite from the substrate with respect to the initial layer, the initial layer is made of a CoCrB-based alloy having a thickness of 1 to 10 nm, and the final layer is made of a Co-based alloy having a thickness of 5 to 30 nm. According to the magnetic recording medium of the present invention, it is possible to make the grain size of the magnetic layer much smaller than the underlayer grain size. Hence, it is possible to realize a magnetic recording medium which can satisfactorily control both the crystallographic c-30 axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.
The magnetic recording medium may further comprise a non-magnetic underlayer disposed between the substrate and the initial layer, where the initial layer nucleates small grain size and uniform grain size distribution in the final layer, so that grain diameters of the final layer are smaller than those of the non-magnetic underlayer.
In the magnetic recording medium, the initial layer may be made of CoCraBbXcYd, where X=Pt, Y=Ta, 30xe2x89xa7a (at %)xe2x89xa715, 8xe2x89xa7b (at %)xe2x89xa71, 15xe2x89xa7c (at %)xe2x89xa70, and 5xe2x89xa7d (at %)xe2x89xa70.
In the magnetic recording medium, the initial layer may be non-magnetic at room temperature.
In the magnetic recording medium, the final layer may be made of a material selected from a group of Co, Fe, Ni and alloys thereof, CoCrTa, CoCrPt, CoCrPtB, CoCrPtTa, CoCrPtW and CoCrPtTaNb.
A further object of the present invention is to provide a magnetic recording medium comprising a substrate, and a magnetic layer disposed above the substrate, where the magnetic layer has an initial layer on a side closer to the substrate, and a final layer on a side opposite to the substrate with respect to the initial layer, the initial layer is made of a CoCrB-based alloy having a B content of 1 at % or greater, and the second layer is made of a Co-based alloy having a B content which is 0 or smaller than the B content of the initial layer. According to the magnetic recording medium of the present invention, it is possible to satisfactorily control both the crystallographic c-axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.
Another object of the present invention is to provide a magnetic recording medium comprising a substrate, and a magnetic layer disposed above the substrate, where the magnetic layer has an initial layer on a side closer to the substrate, and a final layer on a side opposite to the substrate with respect to the initial layer, the initial layer is made of a CoCrX-based alloy, where X is an element or alloy which promotes Cr segregation, and the second layer is made of a Co-based alloy having a X content which is 0 or smaller than the X content of the initial layer. According to the magnetic recording medium of the present invention, it is possible to satisfactorily control both the crystallographic c-axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.
In this case, X may be selected from a group of B, Ag, Cu, C, P and alloys thereof.
Still another object of the present invention is to provide a magnetic storage apparatus comprising at least one magnetic recording medium, and at least one head which records information on and reproducing information from the magnetic recording medium, where the magnetic recording medium comprises a substrate, and a magnetic layer disposed above the substrate, the magnetic layer has an initial layer on a side closer to the substrate, and a final layer on a side opposite from the substrate with respect to the initial layer, the initial layer is made of a CoCrB-based alloy having a thickness of 1 to 10 nm, and the final layer is made of a Co-based alloy having a thickness of 5 to 30 nm. According to the magnetic storage apparatus of the present invention, it is possible to realize satisfactorily control both the crystallographic c-axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.
A further object of the present invention is to provide a magnetic storage apparatus comprising at least one magnetic recording medium, and at least one head which records information on and reproducing information from the magnetic recording medium, where the magnetic recording medium comprises a substrate and a magnetic layer disposed above the substrate, the magnetic layer has an initial layer on a side closer to the substrate, and a final layer on a side opposite to the substrate with respect to the initial layer, the initial layer is made of a CoCrB-based alloy having a B content of 1 at % or greater, and the second layer is made of a Co-based alloy having a B content which is 0 or smaller than the B content of the initial layer. According to the magnetic storage apparatus of the present invention, it is possible to satisfactorily control both the crystallographic c-axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.
Another object of the present invention is to provide a magnetic storage apparatus comprising at least one magnetic recording medium, and at least one head which records information on and reproducing information from the magnetic recording medium, where the magnetic recording medium comprises a substrate and a magnetic layer disposed above the substrate, the magnetic layer has an initial layer on a side closer to the substrate, and a final layer on a side opposite to the substrate with respect to the initial layer, the initial layer is made of a CoCrX-based alloy, where X is an element or alloy which promotes Cr segregation, and the second layer is made of a Co-based alloy having a X content which is 0 or smaller than the X content of the initial layer. According to the magnetic storage apparatus of the present invention, it is possible to satisfactorily control both the crystallographic c-axis orientation and the grain size and size distribution of the magnetic layer, so that improved SNR and high-density recording are obtainable.